Kenji Uchihashi

HITTM cells—high‐efficiency crystalline Si cells with novel structure

Our unique, high-efficiency c-Si solar cell, named the HIT cell, has shown considerable potential to improve junction properties and surface passivation since it was first developed. The improved properties in efficiency and temperature dependence compared to conventional p – n diffused c-Si solar cells are featured in HIT power 21TM solar cell modules and other applications which are now on the market. In the area of research, further improvement in the junction properties of the a-Si/c-Si heterojunction has been examined, and the highest efficiency to date of 20.1% has recently been achieved for a cell size of 101 cm2. The high open circuit voltage exceeding 700 mV, due to the excellent surface passivation of the HIT structure, is responsible for this efficiency. In this paper, recent progress in HIT cells by Sanyo will be introduced. Copyright

Preparation and Properties of a-Si Films Deposited at a High Deposition Rate under a Magnetic Field

An rf plasma decomposition of SiH4 under a magnetic field was investigated. It was confirmed by the optical emission spectra that a high-electron-density plasma can be produced under a magnetic field. High-quality a-Si films with a photosensitivity of σph/σd of 7×105 were obtained at a high deposition rate of 10 A/s under the magnetic field. The a-Si solar cells with i-layers deposited at a high deposition rate under a magnetic field have a higher open-circuit voltage and a higher conversion efficiency than those without the magnetic field; a conversion efficiency of 10.1% under AM1(100mW/cm2) illumination was obtained at a deposition rate of 10 A/s. The rf plasma decomposition of SiH4 under a magnetic field is thought to be very suitable for fabricating a-Si solar cells with a high conversion efficiency at a high deposition rate.

20.7% highest efficiency large area (100.5 cm2) HIT/sup TM/ cell

A world record total area conversion efficiency of 20.7% and high open circuit voltage (VOC) of 719 mV were achieved on a solar cell with HIT (heterojunction with intrinsic thin-layer) structures on both sides (wafer size: 100.5 cm/sup 2/, n-type solar-grade CZ-Si). This solar cell was fabricated with the same process as that used in our mass-production lines. The essence of this high performance is derived from the excellent passivation ability of the HIT structure on c-Si. This report discusses research for excess of 20% efficiency HIT cell (/spl sim/100 cm/sup 2/), focusing on the a-Si passivation effect estimated from the carrier lifetime, and describes product development for the industrialization of HIT cells.

Applications of laser patterning to fabricate innovative thin-film silicon solar cells

In view of the need to obtain high-efficiency and low-cost photovoltaic power generation systems, the electrical series connection of multiple solar cells by laser patterning is a key issue for thin-film silicon solar cells. For a series connection with no thermal damage to the photovoltaic layers, a theoretical analysis of glass-side laser patterning, in which a laser beam is irradiated from the side of a glass substrate, and the optimization of the structure of the solar cells are conducted for a-Si:H/a-SiGe:H stacked solar cells deposited on glass substrates. As a result, an a-Si:H/a-SiGe:H module with both a large area (8,252 cm2) and a conversion efficiency of 11.2% is obtained. Then, to improve efficiency and to reduce cost, the minute structure of microcrystalline silicon (μ c-Si:H) and film-side laser patterning, in which a laser beam is irradiated from the side of the deposited film, are investigated for a-Si:H/μ c-Si:H stacked solar cells deposited on insulator/metal substrates. It is proved that the discontinuity of the doped and photovoltaic layer may cause a reduction in the path density of the leak current, and that this contributes to an improvement in the efficiency of the solar cells. Based on the developed structure, an initial efficiency of 12.6% is obtained in a small-size solar cell. An a-Si:H/μ c-Si:H module (Aperture area = 56.1cm2) with three segments has also been fabricated with an initial efficiency of 11.7% as a first try.

Exchangeable PV shingle

Abstract An “exchangeable photovoltaic (PV) shingle” which is a new type of PV module integrated with a shingle tile has been developed. The new PV shingle tile offers many attractive features, such as a lower total cost, simple construction and maintenance, good design, and fire resistance, compared with previous PV modules. The PV shingles were trial tested and evaluated as PV modules and roofing materials, and no problems appeared. This year, the PV shingles were installed on a model house roof to conduct demonstration tests related to various performance levels for a solar cell system and roofing materials.

Integrated type multi-bandgap a-Si solar cells

Abstract A new type of solar cell, called the “integrated type multi-bandgap a-Si solar cell”, in which stacked type solar cells having different bandgaps are integrated on one substrate, was proposed. Materials, design theory and a processing method were investigated. As a narrow bandgap material, a-SiSn:H was first deposited from a glow discharge reaction, and the photovoltaic effect of a-SiSn:H was observed. As a wide bandgap material, a-SiN:B:H deposited from a glow discharge was found to have good properties for use in solar cells. An optimum design theory for this type of a-Si solar cell was established, and it was found to be useful for the fabrication of the integrated structure.